Polycarbonates have been used as materials in various fields, and as their application fields have become wider, there has arisen a demand for the development of polycarbonates having improved properties.
Electrophotographic photoreceptors recently proposed and used include (1) layered-type organic electrophotographic photoreceptors (OPC), the photosensitive layer of which contains at least two layers, namely a charge generation layer (CGL) for generating charge by exposure and a charge transport layer (CTL) for transporting the charge, and (2) single-layer-type electrophotographic photoreceptors, the photosensitive layer of which is a single layer where charge generating materials and charge transporting materials are dispersed in binder resins. Polycarbonate resins derived from bisphenol A or bisphenol Z have been widely used as the binder resins contained in the charge transport layer of the layered-type electrophotographic photoreceptors and in the photosensitive layer of the single-layer-type electrophotographic photoreceptors. Since the polycarbonate resins derived from bisphenol A or bisphenol Z have good compatibility with charge transporting materials, photoreceptors whose photosensitive layer contains the polycarbonate resins are characterized by their good electrical properties and their relatively high mechanical strength.
In the conventional organic electrophotographic photoreceptors, the photoconductivity of the charge transport layer is improved by dispersing such a large amount of low molecular weight charge transporting materials in the polycarbonate binder resin as to occupy 40 to 50% by weight of the charge transport layer. This causes a problem in that the polycarbonate cannot sufficiently fulfill its function as a binder resin in improving plate wear.
In Japanese Patent Application Kokai Koho (Laid-open) Nos. 1-9964 and 4-31404 are disclosed respectively polyarylamines prepared by polymerizing an arylamine compound, which is a low molecular weight charge transporting material, and styrenic copolymers prepared by using a hydrazone compound as a comonomer. The polyarylamines and the styrenic copolymers having hydrazone units are polymers having photoconductivity themselves, and it has been proposed to solve the above-described problems by substituting them for the conventional charge transporting materials dispersed in the charge transporting layer. The use of such polymers having photoconductivity in themselves as both a charge transporting material and a binder resin in a charge transport layer seems to be effective for solving the above-described problem. However, charge transport layers formed by using the conventional photoconductive polycarbonate (polyarylamine) and styrenic copolymer having hydrazone units suffer from its insufficient plate wear. Further, even the the electrophotographic properties, which are somewhat improved as compared with those of the conventional dispersion type, are not improved sharply.